Method and apparatus for positioning the ventricular lead of a cardiac pacer



Aprxl 28, 1970 J. w. KELLER, JR 3,508,538

METHOD AND APPARATUS FOR POSITIONING THE VENTRICULAR LEAD OF A CARDIAC PACER Filed Nov. 22, 1967 FIG. I

FIG. 3

INVENTOR.

JOHN WALTER KELLER, JR.

AT TO R N EYS United States Patent 3,508,538 METHOD AND APPARATUS FOR POSITIONING THE VENTRICULAR LEAD OF A CARDIAC PACER John Walter Keller, Jr., Miami, Fla., assignor to Cordis Corporation, Miami, Fla., a corporation of Florida Filed Nov. 22, 1967, Ser. No. 685,062 Int. Cl. A61b /02 U.S. Cl. 1282.05 5 Claims ABSTRACT OF THE DISCLOSURE Correct positioning in the heart of the ventricular electrode of a cardiac pacer is determined by inserting a signal-attenuator between the pacer and the electrode. The pulse level of the pacer is reduced by the attenuator by a factor at least as great as the normal post-operative rise in the threshold of ventricular response. The electrode is then repositioned until the attenuated stimulus proves adequate. The attenuator is removed and the pacer is connected directly to the electrode for implantation.

BACKGROUND OF THE INVENTION In implanting cardiac pacers, it is necessary to position an electrode in effective contact with polarizable tissue of the heart for delivery of pulses to stimulate contraction of the ventricles. Originally, the standard surgical approach in implanting cardiac stimulators involved suturing electrodes onto or through the epicardium following a general thoracotomy and invasion of the pericardium.

More recently, there has been extensive use of a pervenous lead, introduced through the venous system into the endocardium. This procedure has the advantage that no major surgery is required, but has as a disadvantage the lack of direct visualization of the electrode placement in its stimulating position. Skilled use of fluoroscopy, combined with interpretation of electrocardiogram signals, is necessary for the successful placement of electrodes into the endocardium to provide long-term stimulation of the heart.

In the majority of implants of this kind, these difficulties are overcome and the electrodes are placed in a suitably sensitive and stable position. However, in a few troublesome cases, the electrodes initially seem to be properly placed but are, in fact, marginal. A post-operative increase in the threshold of response of the ventricles occurs normally, and this may result in the cessation of effective pacing, requiring a second surgical procedure for repositioning the electrodes.

In the pervenous lead system, the electrodes are placed in their final position without a true knowledge of, their proximity to endocardial depolarizable tissue. Consequently, the initial, or acute threshold of stimulation (during implant) can vary widely; observations having been made as low as 0.3 ma. and higher than ma. If the ventricular electrode is left in a position where the acute threshold is as great as 3 or 4 ma., the postoperative or chronic threshold might very well be in excess of the pacer output. Thus, to effect successful pervenous electrode implantation, there must be provision for a measure of the acute threshold value. And the electrode should be so located that this threshold is a factor of at least 5 below the output capability of the stimulator.

Patented Apr. 28, 1970 Surgical and cardiac-catheterization teams generally prefer to minimize the use of complex measuring equipment in the operating area. Further, such equipment is used so seldom in hospitals that its calibration is not generally accurate. And batteries used in the equipment often require replacement just at the time when the equipment is needed. Thus, the requirement that the implanting physician measure the acute thresholds of implanted electrodes imposes considerable burdens.

BRIEF DESCRIPTION OF THE INVENTION It is the primary object of this invention to simplify the accurate placement of the ventricular electrode of a cardiac pacer in effective contact with depolarizable cardiac tissue; and thus to insure that the post-operative intensity of the stimulating pulses will continue to exceed the threshold of ventricular response. Further objects are to simplify the operative procedure in the implanting of cardiac pacers, and to obviate the need for complex equipment and procedures to measure the acute threshold of ventricular response after electrode placement.

According to the invention, the ventricular electrode is first implanted in the heart in a tentative position by conventional techniques, ordinarily by pervenous insertion into the endocardium. I then temporarily connect signalattenuating means of a fixed resistance value between the electrode and a cardiac pacer of any conventional type which may be prescribed. The attenuating means is selected with reference to the open-circuit voltage of the particular pacer, to reduce the current of the pulses supplied to the ventricle by a factor which exceeds the increase in the threshold of response which is normally encountered post-operatively because of the growth of scar tissue. The attenuated pulse level is preferably reduced by a factor of at least five from the output capability of the pacer. A plurality of attenuators having resistance values graduated around a range of interest can also be substituted successively in the pacer-electrode circuit, for a more accurate determination of the true acute current threshold.

In the event that there is inadequate cardiac response to the attenuated pulses, it is only necessary to relocate the electrode until a sufficiently effective contact with depolarizable cardiac tissue is obtained. Subsequently, the attenuator is removed from the circuit, and the ventricular electrode lead is connected directly into the pacer in the usual fashion. The pacer may then be permanently implanted in a subcutaneous pocket, or externally mounted, as appropriate to its type.

The attenuating circuit means may assume the form of a plug, containing the resistance or impedance devices making up the circuit, and having a male contact receivable in the female socket with which the pacer is ordinarily provided for receiving the ventricular lead. The plug may also have a simple pressure clip for temporary attachment to the ventricular lead.

While the specification concludes with claims particularly pointing out the subject matter which I regard as my invention, it is believed that a clearer understanding may be gained from the following detailed description of a preferred embodiment, referring to the accompanying drawings, in which:

FIG. 1 is a schematic view of apparatus arranged according to the invention for testing the acute threshold of an implanted ventricular electrode;

FIG. 2 shows the arrangement of the cardiac pacer and electrode after the completion of the threshold testing procedure, and ready for implantation of the pacer; and

FIG. 3 is a sectional view of attenuating means used in the procedure illustrated in FIG. 1.

In the drawings, a cardiac pacer is generally illustrated at 10, and this may be any of a variety of types as prescribed to suit the patients particular requirements. The pacer comprises a self-contained oscillator circuit and source of potential, for producing electrical pulses for the stimulation of the ventricles. The pulses may, for example, be generated at a fixed rate, or in delayed synchronism with signals produced by contraction of the atrium and received through a further lead (not shown) implanted in the heart. Various types of conventional pacer circuits are described, in Cardiac Pacemakers, by Siddons and Sowton, Charles C. Thomas, Springfield, Ill., 1967. Pacer circuits are well known to those skilled in the art, and no further description thereof is believed necessary to an understanding of the present invention.

The pacer extends into a plug 12, which is provided with sockets for electrical connection to one or more ventricular leads 24, and to an atrial lead where the latter is employed.

The initial step in implanting the pacer system is to extend the lead 24, having a ventricular electrode 26 extending from its end, through an incision 28 into the venous system, and thence into the endocardium of the patients heart. I then connect a signal attenuator 16 into a series circuit between the pacer and the terminal 22 of the lead 24. The attenuator 16 has a shell 17 of insulating material, and a male contact 18 protrudes from one end thereof for insertion into a ventricle lead socket (not shown) in the plug 12 of the pacer. A set screw 14 is provided to grip the contact securely. A conductive spring clamp 20 is secured in the shell 17 for gripping the lead terminal 22. A resistive circuit is formed by a resistor connected between the contact 18 and the clamp 20.

The pacer extends into a plug 12, which is provided either constant current or constant voltage. In either case, a suitable resistance value for the attenuator 16 is found simply by dividing the open circuit voltage of the pacer by a value of stimulating current which is a fraction of its normal maximum output capability, in the range of approximately A; to The post-operative threshold current for ventricular response, or chronic threshold rises by a factor of about 3 to 5 times the initial threshold on implantation. Therefore, the resistance should reduce the pacer output current by a factor which is at least equal to, and preferably greater than, the ratio of the normal output current to the chronic current threshold. The selected factor is preferably at least five. As an example, assume an open-circuit pacer output voltage of 6 volts and a normal output current of 5 ma. Reduction of the output by a factor of five, that is to 1 ma., requires a resistance of approximately 6000 ohms, ignoring the impedance of the lead and electrode.

The contractions of the ventricles are observed by electrocardiogram with the apparatus of FIG. 1 in place. If the stimulation is effective to produce an adequate cardiac response, it can be assumed that the post-operative chronic threshold will be less than the output capability of the pacer, provided only that the electrode 26 remains in its implanted position. In the event, however, that inadequate cardiac stimulation is observed, the surgeon merely repositions the electrode to correct the deficiency. As soon as correct placement has been verified, the attenuator 16 is removed from the circuit, and the lead 24 is plugged directly into the pacer plug'12 as shown in FIG. 2. The terminal 22 extends into a neck or stylet 23, for secure engagement in the plug by means of the set screw 14. Normal procedures are then followed to implant the pacer in a subcutaneous pocket; or it may be mounted externally if appropriate.

A series of the attenuators 16, having different resistance values for reducing the stimulating current by a range of factors, can be successively connected in the circuit of FIG. 1 to provide the physician with a convenient and inexpensive means of determining, as accurately as may be desired, the true current threshold of the implanted electrode.

While I have illustrated and described a preferred mode of practising my improved procedure, and a preferred embodiment of the apparatus, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the invention, which I therefore intend to define in the appended claims without limitation to the details of the illustrated mode and embodiment.

What I claim is:

1. The method of implanting a ventricular electrode in effective contact with cardiac tissue of a patient, for connection to an electrical cardiac pacer circuit to supply ventricular stimuation pulses, which comprises the steps of:

extending a ventricular electrode into contact with cardiac tissue of the patient; connecting signal-attenuating means of fixed resistance value between said electrode and a cardiac pacer circuit to reduce the normal level of pulses supplied by said circuit 'by a factor chosen to exceed a normal post-operative increase in the threshold of ventricular response subsequent to electrode implantation;

determining the resulting cardiac response to the attenuated pulses, and repositioning said electrode as necessary to obtain adequate response;

removing said signal-attenuating means from the circuit, and connecting said electrode directly into said pacer circuit for delivery of pulses at a normal level.

2. The method recited in claim 1, in which said signalattenuating means is chosen to reduce the level of said stimulation pulses by a factor of at least five.

3. The method of determining the approximate threshold of response of a patient to cardiac stimulation pulses supplied by a cardiac pacer circuit through a ventricular electrode, which comprises the steps of:

extending a ventricular electrode into contact with cardiac tissue of the patient;

selecting a series of signal-attenuating means of fixed resistance values and capable of individual connection between said pacer circuit and said electrode to reduce the level of pulses supplied by said circuit by different factors;

individually connecting successive ones of said signalattenuating means between said electrode and said circuit and determining the cardiac response to the resulting levels of stimulating pulses.

4. A threshold tester, for use in cardiac pacer apparatus including circuit means for delivering electrical signal pulses of a predetermined level at intervals and means including a lead for conducting said pulses to the heart of the patient to act as ventricular stimuli, said circuit means having a socket and said lead having a contact for electrical connection there-between;

said threshold tester comprising an insulating shell, a

tester contact for electrical connection in said circuit means socket, clip means for electrical connection with said lead contact, and resistance means connected between said tester contact and said clip means;

said resistance means having a fixed resistance value selected to reduce the level of pulses delivered by said circuit means to said lead by a factor substantially numerically equal to the ratio between the open circuit voltage of said circuit means and an estimated acute threshold current.

5. Cardiac pacer apparatus comprising circuit means for delivering electrical pulses of a predetermined level at intervals,

6 lead means including an electrode for contact with spective means for connection to the circuit means cardiac tissue of a patient to deliver said pulses as connector portion and the lead means connector stimuli to the ventricles of the heart, said circuit portion. means and said lead means being provided with re- References Cited s ective matin rtions of a connector p g 5 UNITED STATES PATENTS and signal-attenuating means of a fixed resistance value for selective connection between said circuit means 3,193,195 19 5 Chardack 123-419 and said lead means, said resistance value being selected to reduce the level of pulses delivered to said OTHER REFERENCES electrode by a factor corresponding to the normal 10 Hopps et 1 S 1, 36, N 4 October 1954, post-operative increase in the threshold of ventricular 3334549 (only 333 m d upon) response subsequent to implantation of said electrode, said signal-attenuating means including also re- WILLIAM E. KAMM, Primary Examiner mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 50 53 Dated April 28 1970 Inventor(s) John W. Keller It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

n the specification, column 3, line 39 should read as follows:

The pacer output oircuit may be designed to deliver.

SIGNED AND SEALED 1'31 6EAL) m IAN R. JR. mm 11, Fleming, 3 Gomiasioner of Patents Attesting Officer 

